An extensive literature exists which describes the biochemical and biophysical properties of human and rat lipoproteins. Other vertebrate and invertebrate systems have been studied less extensively. In light of recent NIH guidelines calling for a reduction in the use of vertebrate animals and an exploration of the possible use of non-vertebrate model systems, it seems timely and appropriate to propose a detailed study of one such model system, the tobacco hornworm, Manduca sexta. The blood of this insect contains a single high density lipoprotein, which is make in the fat body. During the larval stages the lipoprotein contains one copy each of two glycosylated apoproteins (apolipophorin-I, apoLp-I, Mr approximately equal to 250,000 and apolipophorin-II, apoLp-II, Mr approximately equal to 80,000). The lipids are primarily phospholipid and diacylglycerol, which are present in about equimolar amounts. In the adult moth, the lipoprotein contains, in addition to apoLp-I and -II, 2 molecules of a non- glycosylated apoprotein, apoLp-III (Mr equal to 18,400). There are also high concentrations of apoLp-III free in the hemolymph. During flight the adult uses fatty acid as an energy source in flight muscle. The fatty acids are transported from the storage site to the muscle in the form of diacylglycerol via a flight specific lipoprotein. This flight specific lipoprotein is a low density lipoprotein which is derived from the high density lipoprotein by addition of diacylglycerol. In the process of diacylglycerol addition, 14 additional molecules of apoLp-III become associated with the lipoprotein and serve to stabilize the increment of lipid-water interface created by the addition of diacylglycerol. We propose the following specific aims for this grant: 1) a study of the structure-function relationships in apoLp- III: 2) a study of the assembly and secretion of the lipoprotein in both larvae and adults; 3) biochemical and morphological characterization of the fat body during development; 4) a study of the control of apoprotein gene expression; and 5) a study of hormonal control of lipoprotein metabolism.